The overall goal of this proposal is to identify novel serological biomarkers of human colon cancer and evaluate their capacities to predict disease occurrence or clinical outcome. To achieve this goal, we will use a powerful new 4-D protein profiling method recently developed in our lab that can identify many low abundance serum proteins. This method utilizes three tandem orthogonal protein separations consisting of: major protein depletion, solution IEF and 1-D SDS gels. Each gel lane is cut into uniform slices, and digested with trypsin. Each tryptic digest, which still contains many proteins, is then analyzed by LC-MS/MS using a nanocapillary reverse phase column coupled to a high performance linear ion trap mass spectrometer. Candidate human biomarkers in SCID mice bearing human tumors will be identified by distinguishing human and mouse proteins based on species sequence differences. Validation of candidate biomarkers will be conducted in two stages. Initially, candidate human biomarkers will be tested using medium throughput quantitative mass spectrometer assays and Western blots to evaluate sera from a small group of colon cancer patients and matched controls. Higher throughput sandwich ELISA assays will then be developed for the most promising biomarkers, and these assays will be used to systematically test sera from a larger number of early and late stage cancer patients and matched controls. Levels of individual biomarkers as well as groups of biomarkers will be evaluated for their capacity to predict disease occurrence and clinical outcome. This ambitious but feasible five year project involves the following Specific Aims: 1) Identify candidate human colon cancer biomarkers in a SCID mouse xenograph model system using a novel multi-dimensional protein profiling method;2) Validate candidate serum biomarkers in patient and control sera using medium throughput assays;3) Develop high throughput quantitative immunoassays for the most promising biomarkers from initial patient screens;and 4) Compare patient and control serum using high throughput immunoassays. Relevance to public health. Discovery of novel protein biomarkers of colon cancer that can be measured using a simple blood test has great potential to decrease the suffering and loss of life associated with this disease. Recently developed, powerful mass spectrometry-based methods provide a unique opportunity to systematically discovery groups of colon cancer biomarkers. It is most likely that groups of biomarkers (biomarker signatures) will have greater power to monitor cancer than individual biomarkers.